title: Generation of adaptive regulatory T cells by alloantigen is required for some but not all transplant tolerance protocols.
abstract: BACKGROUND
  Because CD4CD25Foxp3 regulatory T cells (Tregs) are essential for the maintenance of self-tolerance, significant interest surrounds the developmental cues for thymic-derived natural Tregs (nTregs) and periphery-generated adaptive Tregs (aTregs). In the transplant setting, the allograft may play a role in the generation of alloantigen-specific Tregs, but this role remains undefined. We examined whether the immune response to a transplant allograft results in the peripheral generation of aTregs.
  
  
  METHODS
  To identify generation of aTregs, purified graft-reactive CD4CD25 T cells were adoptively transferred to mice-bearing skin allograft. To demonstrate that aTregs are necessary for tolerance, DBA/2 skin was transplanted onto C57BL/6-RAG-1-deficient recipients adoptively transferred with purified sorted CD4CD25 T cells; half of the recipients undergo tolerance induction treatment.
  
  
  RESULTS
  By tracking adoptively transferred cells, we show that purified graft-reactive CD4CD25 T lymphocytes up-regulate Foxp3 in mice receiving skin allografts in the absence of any treatment. Interestingly, cotransfer of antigen-specific nTregs suppresses the up-regulation of Foxp3 by inhibiting the proliferation of allograft-responsive T cells. In vitro data are consistent with our in vivo data-Foxp3 cells are generated on antigen activation, and this generation is suppressed on coculture with antigen-specific nTregs. Finally, blocking aTreg generation in grafted, rapamycin-treated mice disrupts alloantigen-specific tolerance induction. In contrast, blocking aTreg generation in grafted mice treated with nondepleting anti-CD4 plus anti-CD40L antibodies does not disrupt graft tolerance.
  
  
  CONCLUSIONS
  We conclude that graft alloantigen stimulates the de novo generation of aTregs, and this generation may represent a necessary step in some but not all protocols of tolerance induction.
authors.affiliation: Department of Surgery, Harvard Medical School, Massachusetts General Hospital, Boston, MA 02114, USA. jkim35@partners.org
authors.forename: James I
authors.initials: JI
authors.lastname: Kim
authors.forename: Matthew R
authors.initials: MR
authors.lastname: O'connor
authors.forename: Patrick E
authors.initials: PE
authors.lastname: Duff
authors.forename: Gaoping
authors.initials: G
authors.lastname: Zhao
authors.forename: Kang Mi
authors.initials: KM
authors.lastname: Lee
authors.forename: Philip
authors.initials: P
authors.lastname: Eliades
authors.forename: Shaoping
authors.initials: S
authors.lastname: Deng
authors.forename: Heidi
authors.initials: H
authors.lastname: Yeh
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Caton
authors.forename: James F
authors.initials: JF
authors.lastname: Markmann
mesh_terms: D000818:Animals; D019013:CD40 Antigens / Q000502:physiology; D023201:CD40 Ligand / Q000502:physiology; D051858:Forkhead Transcription Factors / Q000235:genetics; D007376:Interleukin-2 / Q000494:pharmacology; D007519:Isoantigens / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D020123:Sirolimus / Q000494:pharmacology; D050378:T-Lymphocytes, Regulatory / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D023001:Transplantation Tolerance; D014184:Transplantation, Homologous
chemical_list: D019013:CD40 Antigens; C418974:FOXP3 protein, human; D051858:Forkhead Transcription Factors; D007376:Interleukin-2; D007519:Isoantigens; D016212:Transforming Growth Factor beta; D023201:CD40 Ligand; D020123:Sirolimus